Allows to register a filtered class realm

Only those classes/resoures which match one of the given prefixes are
exposed through the filtered class realm
This closes #69

Author: kwin

src/main/java/org/codehaus/plexus/classworlds/ClassWorld.java

@@ -23,9 +23,11 @@
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Set;
 
 import org.codehaus.plexus.classworlds.realm.ClassRealm;
 import org.codehaus.plexus.classworlds.realm.DuplicateRealmException;
+import org.codehaus.plexus.classworlds.realm.FilteredClassRealm;
 import org.codehaus.plexus.classworlds.realm.NoSuchRealmException;
 
 /**
@@ -64,7 +66,39 @@ public ClassRealm newRealm( String id )
         return newRealm( id, getClass().getClassLoader() );
     }
 
-    public synchronized ClassRealm newRealm( String id, ClassLoader classLoader )
+    public ClassRealm newRealm( String id, ClassLoader classLoader )
+        throws DuplicateRealmException
+    {
+        return newRealm( id, classLoader, Collections.emptySet() );
+    }
+
+    /**
+     * Shortcut for {@link #newRealm(String, ClassLoader, Set)} with the class loader of the current class.
+     * @param id
+     * @param allowedResourceNamePrefixes
+     * @return the created class realm
+     * @throws DuplicateRealmException
+     * @since 2.7.0
+     * @see FilteredClassRealm
+     */
+    public synchronized ClassRealm newRealm( String id, Set<String> allowedResourceNamePrefixes )
+         throws DuplicateRealmException
+    {
+        return newRealm( id, getClass().getClassLoader(), allowedResourceNamePrefixes );
+    }
+
+    /**
+     * Adds a class realm with filtering.
+     * Only resources/classes starting with one of the given prefixes are exposed.
+     * @param id
+     * @param classLoader
+     * @param allowedResourceNamePrefixes the prefixes of resource names which should be exposed. Separator '/' is used here (even for classes).
+     * @return the created class realm
+     * @throws DuplicateRealmException
+     * @since 2.7.0
+     * @see FilteredClassRealm
+     */
+    public synchronized ClassRealm newRealm( String id, ClassLoader classLoader, Set<String> allowedResourceNamePrefixes )
         throws DuplicateRealmException
     {
         if ( realms.containsKey( id ) )
@@ -74,8 +108,14 @@ public synchronized ClassRealm newRealm( String id, ClassLoader classLoader )
 
         ClassRealm realm;
 
-        realm = new ClassRealm( this, id, classLoader );
-
+        if ( allowedResourceNamePrefixes.isEmpty() )
+        {
+            realm = new ClassRealm( this, id, classLoader );
+        }
+        else
+        {
+            realm = new FilteredClassRealm( allowedResourceNamePrefixes, this, id, classLoader );
+        }
         realms.put( id, realm );
 
         for ( ClassWorldListener listener : listeners )
@@ -85,7 +125,7 @@ public synchronized ClassRealm newRealm( String id, ClassLoader classLoader )
 
         return realm;
     }
-
+    
     public synchronized void disposeRealm( String id )
         throws NoSuchRealmException
     {

src/main/java/org/codehaus/plexus/classworlds/realm/ClassRealm.java

@@ -200,7 +200,7 @@ public ClassRealm getParentRealm()
     public ClassRealm createChildRealm( String id )
         throws DuplicateRealmException
     {
-        ClassRealm childRealm = getWorld().newRealm( id, null );
+        ClassRealm childRealm = getWorld().newRealm( id, (ClassLoader) null );
 
         childRealm.setParentRealm( this );
 
@@ -306,6 +306,12 @@ protected Class<?> findClass( String name )
         throw new ClassNotFoundException( name );
     }
 
+    protected Class<?> findClassInternal( String name )
+         throws ClassNotFoundException
+    {
+        return super.findClass( name );
+    }
+
     public URL getResource( String name )
     {
         URL resource = super.getResource( name );
@@ -422,7 +428,7 @@ public Class<?> loadClassFromSelf( String name )
 
                 if ( clazz == null )
                 {
-                    clazz = super.findClass( name );
+                    clazz = findClassInternal( name );
                 }
 
                 return clazz;
@@ -495,7 +501,7 @@ public URL loadResourceFromImport( String name )
 
     public URL loadResourceFromSelf( String name )
     {
-        return super.findResource( name );
+        return findResource( name );
     }
 
     public URL loadResourceFromParent( String name )
@@ -539,7 +545,7 @@ public Enumeration<URL> loadResourcesFromSelf( String name )
     {
         try
         {
-            return super.findResources( name );
+            return findResources( name );
         }
         catch ( IOException e )
         {

src/main/java/org/codehaus/plexus/classworlds/realm/FilteredClassRealm.java

@@ -0,0 +1,92 @@
+package org.codehaus.plexus.classworlds.realm;
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import java.io.IOException;
+import java.net.URL;
+import java.util.Collections;
+import java.util.Enumeration;
+import java.util.Set;
+
+import org.codehaus.plexus.classworlds.ClassWorld;
+
+/**
+ * Similar to {@link ClassRealm} but only exposing some resources of the underlying URL.
+ * Only supposed to be called from {@link ClassWorld}.
+ */
+public class FilteredClassRealm extends ClassRealm
+{
+
+    // no regular expressions for performance reasons
+    private final Set<String> allowedResourceNamePrefixes;
+
+    /**
+     * Creates a new class realm.
+     *
+     * @param allowedResourceNamePrefixes all resources not starting with one of the given prefixes are never exposed through this class loader
+     * @param world The class world this realm belongs to, must not be <code>null</code>.
+     * @param id The identifier for this realm, must not be <code>null</code>.
+     * @param baseClassLoader The base class loader for this realm, may be <code>null</code> to use the bootstrap class
+     *            loader.
+     */
+    public FilteredClassRealm( Set<String> allowedResourceNamePrefixes, ClassWorld world, String id, ClassLoader baseClassLoader )
+    {
+        super( world, id, baseClassLoader );
+        this.allowedResourceNamePrefixes = allowedResourceNamePrefixes;
+    }
+
+    @Override
+    protected Class<?> findClassInternal( String name )
+        throws ClassNotFoundException
+    {
+        String resourceName = name.replace( '.', '/' ).concat( ".class" );
+        if ( !isAllowedName( resourceName ))
+        {
+            throw new ClassNotFoundException(name);
+        }
+        return super.findClassInternal( name );
+    }
+
+    @Override
+    public URL findResource( String name )
+    {
+        if ( !isAllowedName( name ))
+        {
+            return null;
+        }
+        return super.findResource( name );
+    }
+
+    @Override
+    public Enumeration<URL> findResources( String name )
+        throws IOException
+    {
+        if ( !isAllowedName( name ))
+        {
+            return Collections.emptyEnumeration();
+        }
+        return super.findResources( name );
+    }
+
+    private boolean isAllowedName( String name )
+    {
+        return allowedResourceNamePrefixes.stream().anyMatch( name::startsWith );
+    }
+}

src/test/java/org/codehaus/plexus/classworlds/realm/FilteredClassRealmTest.java

@@ -0,0 +1,69 @@
+package org.codehaus.plexus.classworlds.realm;
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import java.util.HashSet;
+import java.util.Set;
+
+import org.codehaus.plexus.classworlds.AbstractClassWorldsTestCase;
+import org.codehaus.plexus.classworlds.ClassWorld;
+import org.junit.Before;
+import org.junit.Test;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertThrows;
+import static org.junit.Assert.assertTrue;
+
+public class FilteredClassRealmTest extends AbstractClassWorldsTestCase
+{
+    private ClassWorld world;
+
+    @Before
+    public void setUp()
+    {
+        this.world = new ClassWorld();
+    }
+
+    @Test
+    public void testLoadClassAndResourcesFiltered()
+        throws Exception
+    {
+        // only allow loading resources whose names start with "a."
+        Set<String> allowedResourcePrefixes = new HashSet<>();
+        allowedResourcePrefixes.add( "a." );
+        allowedResourcePrefixes.add( "a/Aa" );
+        ClassRealm realmA = this.world.newRealm( "realmA",  allowedResourcePrefixes );
+
+        assertThrows( ClassNotFoundException.class, () -> realmA.loadClass( "a.Aa" ) );
+        realmA.addURL( getJarUrl( "a.jar" ) );
+
+        assertNotNull( realmA.loadClass( "a.Aa" ) );
+        assertThrows( ClassNotFoundException.class, () -> realmA.loadClass( "a.A" ) );
+
+        assertNull( realmA.getResource( "common.properties" ) );
+        assertFalse( realmA.getResources( "common.properties" ).hasMoreElements() );
+        
+        assertNotNull( realmA.getResource( "a.properties" ) );
+        assertTrue( realmA.getResources( "a.properties" ).hasMoreElements() );
+    }
+
+}